Vector magnetometry localization of subsurface liquids

ABSTRACT

Systems and methods for locating a subsurface liquid can include an excitation coil configured to induce a magnetic resonance in a subsurface liquid, an array of magnetometers associated with the excitation coil configured to detect a magnetic vector of the magnetic resonance excited subsurface liquid, and a controller in communication with the array of magnetometers and configured to locate the subsurface liquid based on magnetic signals output from the array of magnetometers.

FIELD

The present disclosure generally relates to magnetometers, and moreparticularly, to magneto-optical defect magnetometers, such as diamondnitrogen vacancy magnetometers.

BACKGROUND

A number of industrial applications, as well as scientific areas such asphysics and chemistry can benefit from magnetic detection and imagingwith a device that has extraordinary sensitivity, ability to capturesignals that fluctuate very rapidly (bandwidth) all with a substantivepackage that is extraordinarily small in size, efficient in power andinfinitesimal in volume.

Atomic-sized magneto-optical defect centers, such as nitrogen-vacancy(NV) centers in diamond lattices, have excellent sensitivity formagnetic field measurement and enable fabrication of small magneticsensors that can readily replace existing-technology (e.g., Hall-effect)systems and devices. Magneto-optical defect center materials include butare not be limited to diamonds, Silicon Carbide (SiC), Phosphorous, andother materials with nitrogen, boron, carbon, silicon, or other defectcenters. The diamond nitrogen vacancy (DNV) sensors are maintained inroom temperature and atmospheric pressure and can be even used in liquidenvironments. A green optical source (e.g., a micro-LED) can opticallyexcite NV centers of the DNV sensor and cause emission of fluorescenceradiation (e.g., red light) under off-resonant optical excitation. Amagnetic field generated, for example, by a microwave coil can probetriplet spin states (e.g., with ms=−1, 0, +1) of the NV centers to splitproportional to an external magnetic field projected along the NV axis,resulting in two spin resonance frequencies. The distance between thetwo spin resonance frequencies is a measure of the strength of theexternal magnetic field. A photo detector can measure the fluorescence(red light) emitted by the optically excited NV centers.

SUMMARY

Methods and systems are described for, among other things, a diamondnitrogen vacancy magnetometer.

Some embodiments relate to a system for locating a subsurface liquid.The system includes an excitation coil configured to induce a magneticresonance in a subsurface liquid, an array of magnetometers associatedwith the excitation coil and configured to detect a magnetic vector ofthe magnetic resonance excited subsurface liquid, and a controller incommunication with the array of magnetometers and configured to locatethe subsurface liquid based on magnetic signals output from the array ofmagnetometers.

In some implementations, the array of magnetometers is an array of DNVmagnetometers. In some implementations, the array of magnetometers is anarray of SQUIDs. In some implementations, the excitation coil is aproton spin resonance excitation coil. In some implementations, theexcitation coil and the array of magnetometers are mounted to asubstructure. In some implementations, the controller is configured todeactivate the array of magnetometers during adiabatic passagepreparation of the magnetic resonance signal. In some implementations,deactivating the array of magnetometers comprises deactivating anoptical excitation source. In some implementations, deactivating thearray of magnetometers comprises deactivating a RF excitation source. Insome implementations, deactivating the array of magnetometers comprisesdeactivating an optical excitation source and a RF excitation source. Insome implementations, the controller is configured to record anoscillatory proton (¹H) magnetic resonance (MR) Larmor precession inEarth's field by the array of magnetometers. In some implementations,the controller is configured to filter a local Earth field from amagnetic signal detected by the array of magnetometers. In someimplementations, the filtering comprises periodic filtering (“AC”) pulsesequence operation of the magnetometers. In some implementations, thefiltering comprises reversal of ¹H magnetization in alternating signalco-additions. In some implementations, locating the subsurface liquidincludes the controller generating a numerical location of thesubsurface liquid. In some implementations, locating the subsurfaceliquid includes the controller generating a two-dimensionalreconstruction of the subsurface liquid. In some implementations,locating the subsurface liquid includes the controller generating athree-dimensional reconstruction of the subsurface liquid. In someimplementations, the subsurface liquid is oil. In some implementations,the subsurface liquid is water.

Another implementation relates to a method for locating a subsurfaceliquid. The method includes activating a proton spin resonanceexcitation coil, activating an array of magnetometers, recording anoscillatory ¹H MR precession in Earth's field by the array ofmagnetometers, and generating a location of the subsurface liquid basedon the recorded oscillatory ¹H MR precession.

In some implementations, the array of magnetometers is an array of DNVmagnetometers. In some implementations, the array of magnetometers is anarray of SQUIDs. In some implementations, the proton spin resonanceexcitation coil and the array of magnetometers are mounted to asubstructure. In some implementations, the method further includesdeactivating the array of magnetometers during adiabatic passagepreparation. In some implementations, deactivating the array ofmagnetometers comprises deactivating an optical excitation source. Insome implementations, deactivating the array of magnetometers comprisesdeactivating a RF excitation source. In some implementations,deactivating the array of magnetometers comprises deactivating anoptical excitation source and a RF excitation source. In someimplementations, the method further includes filtering a local Earthfield from a magnetic signal detected by the array of magnetometers. Insome implementations, the filtering includes AC filtering pulsesequence. In some implementations, the filtering includes reversal of ¹Hmagnetization in alternating signal co-additions. In someimplementations, generating a location of the subsurface liquid includesgenerating a numerical location of the subsurface liquid. In someimplementations, generating a location of the subsurface liquid includesgenerating a two-dimensional reconstruction of the subsurface liquid. Insome implementations, generating a location of the subsurface liquidincludes generating a three-dimensional reconstruction of the subsurfaceliquid. In some implementations, the subsurface liquid is oil. In someimplementations, the subsurface liquid is water.

A further implementation relates to an apparatus. The apparatus includesa substructure, a proton spin resonance excitation coil mounted to thesubstructure and configured to induce a magnetic resonance in asubsurface liquid, an array of DNV magnetometers mounted to thesubstructure and configured to detect a magnetic vector of the magneticresonance excited subsurface liquid, and a controller in communicationwith the array of magnetometers. The controller is configured to recordan oscillatory ¹H MR precession in Earth's field by the array ofmagnetometers and locate the subsurface liquid based on magnetic signalsoutput from the array of magnetometers.

In some implementations, the controller is configured to deactivate thearray of DNV magnetometers during adiabatic passage preparation. In someimplementations, deactivating the array of magnetometers comprisesdeactivating an optical excitation source. In some implementations,deactivating the array of magnetometers comprises deactivating a RFexcitation source. In some implementations, deactivating the array ofmagnetometers comprises deactivating an optical excitation source and aRF excitation source. In some implementations, the controller is furtherconfigured to filter a local Earth field from a magnetic signal detectedby the array of magnetometers. In some implementations, the filteringcomprises AC filtering pulse sequence. In some implementations, thefiltering comprises reversal of ¹H magnetization in alternating signalco-additions. In some implementations locating the subsurface liquidincludes the controller generating a numerical location of thesubsurface liquid. In some implementations, locating the subsurfaceliquid includes the controller generating a two-dimensionalreconstruction of the subsurface liquid. In some implementations,locating the subsurface liquid includes the controller generating athree-dimensional reconstruction of the subsurface liquid. In someimplementations, the subsurface liquid is oil. In some implementations,the subsurface liquid is water.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,aspects, and advantages will become apparent from the description, thedrawings, and the claims, in which:

FIG. 1 illustrates an orientation of an NV center in a diamond lattice;

FIG. 2 illustrates an energy level diagram showing energy levels of spinstates for the NV center;

FIG. 3 illustrates a schematic diagram of a NV center magnetic sensorsystem;

FIG. 4 is a graph illustrating the fluorescence as a function of anapplied RF frequency of an NV center along a given direction for a zeromagnetic field, and also for a non-zero magnetic field having acomponent along the NV axis;

FIG. 5 is a graph illustrating the fluorescence as a function of anapplied RF frequency for four different NV center orientations for anon-zero magnetic field;

FIG. 6 is an illustrative overview of a system for localization of asubsurface liquid using a proton spin resonance excitation coil forinducing a magnetization in the subsurface liquid and an array of vectormagnetometers to detect the location of the subsurface liquid;

FIG. 7 is an illustrative overview of sets of magnetometers of FIG. 6outputting detection signals from the magnetized subsurface liquid;

FIG. 8 is an illustrative view depicting the detected location of thesubsurface liquid based on the detection signals from the sets ofmagnetometers of FIG. 7; and

FIG. 9 is a process diagram for an illustrative process for detectingthe location of the subsurface liquid using the array of magnetometers.

It will be recognized that some or all of the figures are schematicrepresentations for purposes of illustration. The figures are providedfor the purpose of illustrating one or more embodiments with theexplicit understanding that they will not be used to limit the scope orthe meaning of the claims.

DETAILED DESCRIPTION

In some aspects, methods and systems are disclosed for detecting thelocation of a subsurface liquid using an array of magnetometers. In someinstances, the magnetometers may include diamond nitrogen-vacancymagnetometers.

Nitrogen-vacancy centers (NV centers) are defects in a diamond's crystalstructure, which can purposefully be manufactured in synthetic diamondsas shown in FIG. 1. In general, when excited by green light andmicrowave radiation, the NV centers cause the diamond to generate redlight. When excited with green light, the NV centers generate red lightfluorescence. After sufficient time (on order of nanoseconds tomicroseconds) the fluorescence counts stabilize. When microwaveradiation is added, the NV electron spin states are changed, and thisresults in a change in intensity of the red fluorescence. The changes influorescence are recorded as a measure of electron spin resonance. Thistechnique is known as “optically detected magnetic resonance” or ODMR.By measuring the changes, the NV centers can be used to accuratelydetect the magnetic field strength.

The NV center may exist in a neutral charge state or a negative chargestate. Conventionally, the neutral charge state uses the nomenclatureNV⁰, while the negative charge state uses the nomenclature NV, which isadopted in this description.

The NV center has a number of electrons, including three unpairedelectrons, each one from the vacancy to a respective of the three carbonatoms adjacent to the vacancy, and a pair of electrons between thenitrogen and the vacancy. The NV center, which is in the negativelycharged state, also includes an extra electron.

The NV center has rotational symmetry and, as shown in FIG. 2, has aground state, which is a spin triplet with ³A₂ symmetry with one spinstate m_(s)=0, and two further spin states m_(s)=+1, and m_(s)=−1. Inthe absence of an external magnetic field, the m_(s)=±1 energy levelsare offset from the m_(s)=0 due to spin-spin interactions, and them_(s)=±1 energy levels are degenerate, i.e., they have the same energy.The m_(s)=0 spin state energy level is split from the m_(s)=±1 energylevels by an energy of approximately 2.87 GHz for a zero externalmagnetic field.

Introducing an external magnetic field with a component along the NVaxis lifts the degeneracy of the m_(s)=±1 energy levels, splitting theenergy levels m_(s)=±1 by an amount 2 gμ_(B)Bz, where g is the Landeg-factor, μ_(B) is the Bohr magneton, and Bz is the component of theexternal magnetic field along the NV axis. This relationship is correctto a first order and inclusion of higher order corrections is astraightforward matter and will not affect the computational and logicsteps in the systems and methods described below.

The NV center electronic structure further includes an excited tripletstate ³E with corresponding m_(s)=0 and m_(s)=±1 spin states. Theoptical transitions between the ground state ³A₂ and the excited triplet³E are predominantly spin conserving, meaning that the opticaltransitions are between initial and final states that have the samespin. For a direct transition between the excited triplet ³E and theground state ³A₂, a photon of red light is emitted with a photon energycorresponding to the energy difference between the energy levels of thetransitions.

There is, however, an alternative non-radiative decay route from thetriplet ³E to the ground state ³A₂ via intermediate electron states,which are thought to be intermediate singlet states A, E withintermediate energy levels. Significantly, the transition rate from them_(s)=±1 spin states of the excited triplet ³E to the intermediateenergy levels is significantly greater than the transition rate from them_(s)=0 spin state of the excited triplet ³E to the intermediate energylevels. The transition from the singlet states A, E to the ground statetriplet ³A₂ predominantly decays to the m_(s)=0 spin state over them_(s)=±1 spins states. These features of the decay from the excitedtriplet ³E state via the intermediate singlet states A, E to the groundstate triplet ³A₂ allows that if optical excitation is provided to thesystem, the optical excitation will eventually pump the NV center intothe m_(s)=0 spin state of the ground state ³A₂. In this way, thepopulation of the m_(s)=0 spin state of the ground state ³A₂ may be“reset” to a maximum polarization determined by the decay rates from thetriplet ³E to the intermediate singlet states.

Another feature of the decay is that the fluorescence intensity due tooptically stimulating the excited triplet ³E state is less for them_(s)=±1 states than for the m_(s)=0 spin state. This is so because thedecay via the intermediate states does not result in a photon emitted inthe fluorescence band, and because of the greater probability that them_(s)=±1 states of the excited triplet ³E state will decay via thenon-radiative decay path. The lower fluorescence intensity for them_(s)=±1 states than for the m_(s)=0 spin state allows the fluorescenceintensity to be used to determine the spin state. As the population ofthe m_(s)=±1 states increases relative to the m_(s)=0 spin, the overallfluorescence intensity will be reduced.

FIG. 3 is a schematic diagram illustrating a NV center magnetic sensorsystem 300 that uses fluorescence intensity to distinguish the m_(s)=±1states, and to measure the magnetic field based on the energy differencebetween the m_(s)=+1 state and the m_(s)=−1 state, as manifested by theRF frequencies corresponding to each state. The system 300 includes anoptical excitation source 310, which directs optical excitation to an NVdiamond material 320 with NV centers. The system further includes an RFexcitation source 330, which provides RF radiation to the NV diamondmaterial 320. Light from the NV diamond may be directed through anoptical filter 350 to an optical detector 340.

The RF excitation source 330 may be a microwave coil, for example. TheRF excitation source 330, when emitting RF radiation with a photonenergy resonant with the transition energy between ground m_(s)=0 spinstate and the m_(s)=+1 spin state, excites a transition between thosespin states. For such a resonance, the spin state cycles between groundm_(s)=0 spin state and the m_(s)=+1 spin state, reducing the populationin the m_(s)=0 spin state and reducing the overall fluorescence atresonances. Similarly, resonance and a subsequent decrease influorescence intensity occurs between the m_(s)=0 spin state and them_(s)=−1 spin state of the ground state when the photon energy of the RFradiation emitted by the RF excitation source is the difference inenergies of the m_(s)=0 spin state and the m_(s)=−1 spin state.

The optical excitation source 310 may be a laser or a light emittingdiode, for example, which emits light in the green (light having awavelength such that the color is green), for example. The opticalexcitation source 310 induces fluorescence in the red, which correspondsto an electronic transition from the excited state to the ground state.Light from the NV diamond material 320 is directed through the opticalfilter 350 to filter out light in the excitation band (in the green, forexample), and to pass light in the red fluorescence band, which in turnis detected by the detector 340. The optical excitation light source310, in addition to exciting fluorescence in the diamond material 320,also serves to reset the population of the m_(s)=0 spin state of theground state ³A₂ to a maximum polarization, or other desiredpolarization.

For continuous wave excitation, the optical excitation source 310continuously pumps the NV centers, and the RF excitation source 330sweeps across a frequency range that includes the zero splitting (whenthe m_(s)=±1 spin states have the same energy) photon energy ofapproximately 2.87 GHz. The fluorescence for an RF sweep correspondingto a diamond material 320 with NV centers aligned along a singledirection is shown in FIG. 4 for different magnetic field components Bzalong the NV axis, where the energy splitting between the m_(s)=−1 spinstate and the m_(s)=+1 spin state increases with Bz. Thus, the componentBz may be determined. Optical excitation schemes other than continuouswave excitation are contemplated, such as excitation schemes involvingpulsed optical excitation, and pulsed RF excitation. Examples of pulsedexcitation schemes include Ramsey pulse sequence (described in moredetail below), and spin echo pulse sequence.

In general, the diamond material 320 will have NV centers aligned alongdirections of four different orientation classes. FIG. 5 illustratesfluorescence as a function of RF frequency for the case where thediamond material 320 has NV centers aligned along directions of fourdifferent orientation classes. In this case, the component Bz along eachof the different orientations may be determined. These results, alongwith the known orientation of crystallographic planes of a diamondlattice, allow not only the magnitude of the external magnetic field tobe determined, but also the direction of the magnetic field.

While FIG. 3 illustrates an NV center magnetic sensor system 300 with NVdiamond material 320 with a plurality of NV centers, in general, themagnetic sensor system may instead employ a different magneto-opticaldefect center material, with a plurality of magneto-optical defectcenters. Magneto-optical defect center materials include but are not belimited to diamonds, Silicon Carbide (SiC), Phosphorous, and othermaterials with nitrogen, boron, carbon, silicon, or other defectcenters. The electronic spin state energies of the magneto-opticaldefect centers shift with magnetic field, and the optical response, suchas fluorescence, for the different spin states is not the same for allof the different spin states. In this way, the magnetic field may bedetermined based on optical excitation, and possibly RF excitation, in acorresponding way to that described above with NV diamond material.

FIG. 6 depicts an overview of a system 600 for localization of asubsurface liquid 690 using a proton spin resonance excitation coil 610for inducing a magnetization in the subsurface liquid 690, an array 620of vector magnetometers 622 to detect the location of the subsurfaceliquid 690, and a controller 650 for generating a location,two-dimensional reconstruction, and/or three-dimensional reconstructionof the subsurface liquid 690 based on the output of the array 620 ofvector magnetometers 622. The subsurface liquid 690 may be a liquid ofinterest for the location, such as oil, other hydrocarbons, water, orother liquids. For instance, oil may be of interest in artic, Antarctic,tundra, and/or other locations where oil and water may be mixed. Inparticular, locating oil during an oil spill may be important forrecovery and/or clean-up procedures. In certain locations, such as thearctic, Antarctic, and/or other ice or snow areas, visual location ofthe oil may be difficult as the oil may be below the surface, such asmixed in and/or below snow or ice, underground, in water under ice, etc.Moreover, site surveys can be expensive, dangerous, and/or ineffectivefor remote and/or difficult to reach areas. Accordingly, accuratelocating of the oil may be useful to expedite recovery, containment,and/or clean-up efforts for spilled oil. In other instances, subsurfaceoil can be located for extraction purposes. In further instances,subsurface water can be located in arid or other geographic locationsfor extraction and use.

The proton spin resonance excitation coil 610 is a coil for inducingmagnetic resonance in the subsurface liquid 690, such as oil, bygenerating a magnetic resonance (MR) field from the coil. The protonspin resonance excitation coil 610 may be a flat coil, such as a flatfigure-8gradiometer coil such as that described in L. Chavez, et al.,“Detecting Arctic oil spills with NMR: α feasibility study”, NearSurface Geophysics, Vol 13, No 4, August 2015, the disclosure of whichis incorporated by reference in its entirety herein. The proton spinresonance excitation coil 610 is configured to induce magnetic ¹Hmagnetic resonance in the subsurface liquid 690 and any other differentliquids below the position of the proton spin resonance excitation coil610. By exploiting the magnetic relaxation differential between thesubsurface liquid of interest and any other liquids near the subsurfaceliquid of interest, a general location of the subsurface liquid can beestimated. In some implementations, the proton spin resonance excitationcoil 610 may be mounted to a substructure, such as a tubular frame,piping, or other substructure to maintain the coil 610 configuration andshape. In some instances, the substructure may be coupled to a vehicle,such as a helicopter, or other device to move the substructure and theproton spin resonance excitation coil 610. The proton spin resonanceexcitation coil 610 is a large scale coil, such as on the order of 10meters, and may be difficult to detect a particular location of thesubsurface liquid 690. Accordingly, an array 620 of magnetometers 622may be implemented with the proton spin resonance excitation coil 610 toexploit the magnetic resonance excitation from the proton spin resonanceexcitation coil 610 and detected a location of the subsurface liquid 690using the vector signals from sets of magnetometers 622.

The array 620 of the magnetometers 622 may be mounted to thesubstructure to which the proton spin resonance excitation coil 610 ismounted and/or may be independent of the proton spin resonanceexcitation coil 610. The array 620 is generally positioned in a circulararrangement relative to the proton spin resonance excitation coil 610,but the array 620 may have other geometric configurations, such assquare, rectangular, triangular, ovular, etc. Other possible arrayconfigurations may include a two-dimensional array filling a circulararea subtended by the excitation coil or a three-dimensional arraypositioned above or below the excitation coil with an area projectedwithin the coil. The magnetometers 622 of the present disclosure are DNVmagnetometers, but other vector magnetometry devices may be utilized aswell, such as superconducting quantum interference devices (SQUIDs).Such SQUID devices are described in greater detail in L Q Qiu, et al,“SQUID-detected NMR in Earth's Magnetic Field”, 8th European Conferenceon Applied Superconductivity (ELICAS 2007), Journal of Physics:Conference Series 97 (2008) 012026, IOP Publishing; A. N. Matlashov, etal., “SQUIDs for Magnetic Resonance Imaging at Ultra-low MagneticField”, PIERS online 5.5 (2009); and/or J. Clarke, et al.,“SQUID-Detected Magnetic Resonance Imaging in Microtesla Fields”, AnnualReview of Biomedical Engineering, Vol. 9: 389-413 (2007), thedisclosures of which are incorporated by reference herein in theirentirety. In some implementations, the array of magnetometers is anarray of gas-cell detectors.

The controller 650 is electrically coupled to and/or in communicationwith the array 620 of magnetometers 622 and, in some implementations,the proton spin resonance excitation coil 610 to control themagnetometers 622 and, optionally, the proton spin resonance excitationcoil 610. In addition, the controller 650 is configured to utilize theoutput from the magnetometers 622 to generate a location,two-dimensional reconstruction, and/or three-dimensional reconstructionof the subsurface liquid 690 as will be described in greater detail inreference to FIG. 9.

Referring to FIG. 7, once the proton spin resonance excitation coil 610induces a magnetic resonance in the subsurface liquid 690, the array 620of magnetometers 622 can be activated to detect the magnetic fieldvectors of the subsurface liquid 690. As shown in FIG. 7, sets 630, 632,634, 636 of magnetometers 622 may be utilized to determine detectedmagnetic vectors, M, and magnetic intensity, |M|, for the magnetizedsubsurface liquid 690. The detected magnetic vectors and magneticintensity can be determined by detecting the Earth's magnetic field atthe location without the subsurface liquid 690 being magnetized andremoving the result from the magnetic signal detected by themagnetometers 622 once the subsurface liquid 690 is magnetized by theproton spin resonance excitation coil 610. In other implementations, themagnetometers can be operated in a mode that filters out magnetic fieldswhich are effectively static, such as the Earth's field, on the timescale of the magnetometer measurements (typically miliseconds). Themagnetic intensity, |M|, is proportional to the distance of thesubsurface liquid 690 relative to each magnetometer 622 and/or set ofmagnetometers 630, 632, 634, 636. In some implementations, atime-varying nuclear magnetic resonance, M(t), can be modeled as aradiating source, such as a dipole radiator. The magnetic vector, M,provides a direction of the subsurface liquid 690 relative to eachmagnetometer 622 and/or set of magnetometers 630, 632, 634, 636. Usingthe foregoing, a back-projection or other reconstruction algorithm canbe implemented to locate the subsurface liquid 690, as shown in FIG. 8,from the magnetic vector and/or magnetic intensity measured by 1 throughN magnetometers 622 and/or sets of magnetometers 622.

FIG. 9 depicts a process 700 for utilizing the proton spin resonanceexcitation coil 610 and array 620 of magnetometers 622 to detect thesubsurface liquid 690. The process 700 may be implemented by controller650 of FIG. 6. The process 700 includes deactivating or “blanking” themagnetometers (block 702). The deactivation or “blanking” may includedeactivating an optical excitation source, such as optical excitationsource 310 of FIG. 3, for a DNV magnetometer and/or deactivating a RFexcitation source, such as RF excitation source 330 of FIG. 3.Deactivating the optical and/or RF excitation source occurs during theadiabatic passage preparation with the proton spin resonance excitationcoil 610. Thus, the magnetometers 622 are not affected by the protonspin resonance excitation coil 610.

The process 700 further includes activating the proton spin resonanceexcitation coil 610 (block 704). Activating the proton spin resonanceexcitation coil 610 induces a magnetic resonance in the subsurfaceliquid 690 that will be measured by the magnetometers 622. The process700 further includes activating the magnetometers 622 (block 706). Formagnetometers such as DNV magnetometers, the activation step can berapid after the proton spin resonance excitation coil 610 isdeactivated. That is, the rapid “turn on” time for DNV magnetometers canbe used to detect the magnetic signal from the magnetic resonant excitedsubsurface liquid 690 quickly after the excitation coil 610 isdeactivated, allowing for a larger magnetic signal (and therefore a moreeasily discernable magnetic signal) to be detected than othermagnetometers. The process 700 further includes recording theoscillatory ¹H MR precession in Earth's field by the magnetometers(block 708). The process 700 further includes filtering the local,approximately static, Earth field from the magnetic signal detected bythe magnetometers (block 710). In some implementations, the filteringmay discriminate the magnetic signal of the subsurface liquid 690 fromthe local Earth field by AC filtering pulse sequence, such as Hahn Echo.In other implementations, the filtering may use a reversal of ¹Hmagnetization in alternating signal co-additions to enhancediscrimination of the magnetic signal of the subsurface liquid 690relative to the local Earth field. The process 700 includes generating alocation, a two-dimensional reconstruction, and/or a three-dimensionalreconstruction of the subsurface liquid 690 based on the filteredmagnetic signal from the magnetometers (block 712). The generation ofthe location (e.g., scalar or numerical location), two-dimensionalreconstruction, and/or three-dimensional reconstruction may be through aback-projection and/or tomographic algorithm for image reconstruction,such as those similar to magnetic resonance imaging (MRI) and/orcomputed tomography (CT).

The foregoing description is provided to enable a person skilled in theart to practice the various configurations described herein. While thesubject technology has been particularly described with reference to thevarious figures and configurations, it should be understood that theseare for illustration purposes only and should not be taken as limitingthe scope of the subject technology.

While the above discussion primarily refers to circuits and/orcircuitry, the circuits may include a microprocessor or multi-coreprocessors that execute software, one or more implementations areperformed by one or more integrated circuits, such as applicationspecific integrated circuits (ASICs) or field programmable gate arrays(FPGAs). In one or more implementations, such integrated circuitsexecute instructions that are stored on the circuit itself.

The description of the subject technology is provided to enable anyperson skilled in the art to practice the various embodiments describedherein. While the subject technology has been particularly describedwith reference to the various figures and embodiments, it should beunderstood that these are for illustration purposes only and should notbe taken as limiting the scope of the subject technology.

There may be many other ways to implement the subject technology.Various functions and elements described herein may be partitioneddifferently from those shown without departing from the scope of thesubject technology. Various modifications to these embodiments may bereadily apparent to those skilled in the art, and generic principlesdefined herein may be applied to other embodiments. Thus, many changesand modifications may be made to the subject technology, by one havingordinary skill in the art, without departing from the scope of thesubject technology.

A reference to an element in the singular is not intended to mean “oneand only one” unless specifically stated, but rather “one or more.” Theterm “some” refers to one or more. Underlined and/or italicized headingsand subheadings are used for convenience only, do not limit the subjecttechnology, and are not referred to in connection with theinterpretation of the description of the subject technology. Allstructural and functional equivalents to the elements of the variousembodiments described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and intended to be encompassed by thesubject technology. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the above description.

What is claimed is:
 1. An apparatus comprising: a substructure; a protonspin resonance excitation coil mounted to the substructure andconfigured to induce a magnetic resonance in a subsurface liquid; anarray of DNV magnetometers mounted to the substructure and configured todetect a magnetic vector of the magnetic resonance excited subsurfaceliquid; and a controller in communication with the array ofmagnetometers and configured to: record an oscillatory proton (¹H)magnetic resonance (MR) Larmor precession in Earth's field by the arrayof magnetometers, and locate the subsurface liquid based on magneticsignals output from the array of magnetometers.
 2. The apparatus ofclaim 1, wherein the controller is configured to deactivate the array ofDNV magnetometers during adiabatic passage preparation of a magneticresonance signal of the proton spin resonance excitation coil.
 3. Theapparatus of claim 2, wherein deactivating the array of magnetometerscomprises deactivating an optical excitation source.
 4. The apparatus ofclaim 2, wherein deactivating the array of magnetometers comprisesdeactivating a RF excitation source.
 5. The apparatus of claim 2,wherein deactivating the array of magnetometers comprises deactivatingan optical excitation source and a RF excitation source.
 6. Theapparatus of claim 1, wherein the controller is further configured tofilter a local Earth field from a magnetic signal detected by the arrayof magnetometers.
 7. The apparatus of claim 6, wherein the filteringcomprises periodic filtering (“AC”) pulse sequence operation of thearray of DNV magnetometers.
 8. The apparatus of claim 6, wherein thefiltering comprises reversal of ¹H magnetization in alternating signalco-additions.
 9. The apparatus of claim 6, wherein locating thesubsurface liquid includes the controller generating a numericallocation of the subsurface liquid.
 10. The apparatus of claim 6, whereinlocating the subsurface liquid includes the controller generating atwo-dimensional reconstruction of the subsurface liquid.
 11. Theapparatus of claim 6, wherein locating the subsurface liquid includesthe controller generating a three-dimensional reconstruction of thesubsurface liquid.
 12. The apparatus of claim 1, wherein the subsurfaceliquid is oil.
 13. The apparatus of claim 1, wherein the subsurfaceliquid is water.
 14. A system for locating a subsurface liquid, thesystem comprising: an excitation coil configured to induce a magneticresonance in a subsurface liquid; an array of magnetometers associatedwith the excitation coil, the array of magnetometers configured todetect a magnetic vector of the magnetic resonance excited subsurfaceliquid; and a controller in communication with the array ofmagnetometers and configured to locate the subsurface liquid based onmagnetic signals output from the array of magnetometers.
 15. The systemof claim 14, wherein the array of magnetometers is an array of DNVmagnetometers.
 16. The system of claim 14, wherein the array ofmagnetometers is an array of SQUIDs.
 17. The system of claim 14, whereinthe excitation coil is a proton spin resonance excitation coil.
 18. Thesystem of claim 14, wherein the excitation coil and the array ofmagnetometers are mounted to a substructure.
 19. The system of claim 14,wherein the controller is configured to deactivate the array ofmagnetometers during adiabatic passage preparation of a magneticresonance signal of the excitation coil.
 20. The system of claim 19,wherein deactivating the array of magnetometers comprises deactivatingan optical excitation source.
 21. The system of claim 19, whereindeactivating the array of magnetometers comprises deactivating a RFexcitation source.
 22. The system of claim 19, wherein deactivating thearray of magnetometers comprises deactivating an optical excitationsource and a RF excitation source.
 23. The system of claim 14, whereinthe controller is configured to record an oscillatory proton (¹H)magnetic resonance (MR) Larmor precession in Earth's field by the arrayof magnetometers.
 24. The system of claim 23, wherein the controller isconfigured to filter a local Earth field from a magnetic signal detectedby the array of magnetometers.
 25. The system of claim 24, wherein thefiltering comprises periodic filtering (“AC”) pulse sequence operationof the array of magnetometers.
 26. The system of claim 24, wherein thefiltering comprises reversal of ¹H magnetization in alternating signalco-additions.
 27. The system of claim 14, wherein locating thesubsurface liquid includes the controller generating a numericallocation of the subsurface liquid.
 28. The system of claim 14, whereinlocating the subsurface liquid includes the controller generating atwo-dimensional reconstruction of the subsurface liquid.
 29. The systemof claim 14, wherein locating the subsurface liquid includes thecontroller generating a three-dimensional reconstruction of thesubsurface liquid.
 30. The system of claim 14, wherein the subsurfaceliquid is oil.
 31. The system of claim 14, wherein the subsurface liquidis water.
 32. A method for locating a subsurface liquid comprising:activating a proton spin resonance excitation coil; activating an arrayof magnetometers; recording an oscillatory proton (¹H) magneticresonance (MR) Larmor precession in Earth's field by the array ofmagnetometers; and generating a location of the subsurface liquid basedon the recorded oscillatory proton (¹H) magnetic resonance (MR) Larmorprecession.
 33. The method of claim 32, wherein the array ofmagnetometers is an array of DNV magnetometers.
 34. The method of claim32, wherein the array of magnetometers is an array of SQUIDs.
 35. Themethod of claim 32, wherein the proton spin resonance excitation coiland the array of magnetometers are mounted to a substructure.
 36. Themethod of claim 32 further comprising deactivating the array ofmagnetometers during adiabatic passage preparation of a magneticresonance signal of the proton spin resonance excitation coil.
 37. Themethod of claim 36, wherein deactivating the array of magnetometerscomprises deactivating an optical excitation source.
 38. The method ofclaim 36, wherein deactivating the array of magnetometers comprisesdeactivating a RF excitation source.
 39. The method of claim 36, whereindeactivating the array of magnetometers comprises deactivating anoptical excitation source and a RF excitation source.
 40. The method ofclaim 32 further comprising filtering a local Earth field from amagnetic signal detected by the array of magnetometers.
 41. The methodof claim 40, wherein the filtering comprises periodic filtering (“AC”)pulse sequence operation of the array of magnetometers.
 42. The methodof claim 40, wherein the filtering comprises reversal of ¹Hmagnetization in alternating signal co-additions.
 43. The method ofclaim 32, wherein generating a location of the subsurface liquidincludes generating a numerical location of the subsurface liquid. 44.The method of claim 32, wherein generating a location of the subsurfaceliquid includes generating a two-dimensional reconstruction of thesubsurface liquid.
 45. The method of claim 32, wherein generating alocation of the subsurface liquid includes generating athree-dimensional reconstruction of the subsurface liquid.
 46. Themethod of claim 32, wherein the subsurface liquid is oil.
 47. The methodof claim 32, wherein the subsurface liquid is water.